1. Field of the Invention
The present invention relates to an improvement in jaw crusher. More particularly, the present invention relates to a jaw crusher for breaking asphalt pavement wastes, concrete scraps, etc which has a pass-through preventing device to prevent an object of crushing from passing through the area between a fixed tooth plate and a movable tooth plate without being crushed, together with a crushing tooth plate structure that is improved in the crushing performance.
2. Description of the Prior Art
Jaw crushers are known and used as machines for breaking rocks, asphalt pavement wastes, concrete scraps, etc. into pieces of desired size. These days, a large amount of concrete scrap and asphalt pavement waste are produced by dismantling of concrete buildings, repair of asphalt pavements, etc. Treatment of these wastes, particularly in urban areas, gives rise to a social problem because of the generation of noise and dust during the treatment, difficulty in securing a place for dumping wastes, a high cost of waste transportation, etc.
For this reason, these wastes are desired to be speedily treated and reused at or near the site where the wastes are produced, as much as possible When such wastes are crushed with a jaw crusher, a thin waste material may pass through the crushing space between a fixed tooth plate and a movable tooth plate to come out of a discharge opening without being crushed. When the lower end portion of the fixed or movable tooth plate has become worn, the size of the discharge opening enlarges, so that a plate-shaped waste material, for example, a concrete lid for a road side ditch, may pass through the crushing space to drop out of the discharge opening without being crushed.
A jaw crusher wherein a square bar is disposed in an outlet of an object of crushing not to prevent the object from passing through without being crushed but to control the size of pieces of the crushed object is known as Japanese Utility Model Laid-Open (KOKAI) No. 63-185453 (Date of public disclosure: Nov. 29, 1988; Applicant: Sankyo Kikai K. K.). In this mechanism, no retracting mechanism is provided and hence the square bar is constantly exposed to the object of crushing.
To crush non-rigid objects, for example, asphalt, it has been conventional practice to use tooth plate structures shown in FIGS. 10(a) and 10(b), which are designed to crush rigid objects, e.g., aggregates, concrete, etc., or a tooth plate structure shown in FIG. 10(c), which is devised to crush non-rigid objects. However, in these prior arts, a groove-shaped recess 86 is defined between a cheek plate 80 that is attached to a side plate of a machine frame and a fixed tooth plate 85a that is attached to the machine body, as shown in FIGS. 10(a), 10(b) and 10(c).
For this reason, a non-rigid object is pressed by a movable tooth plate 85b that is attached to a swing frame in such a manner that the object is confined in the recess 86, resulting in the object sticking to the cheek plate 80, the fixed tooth plate 85a and the movable tooth plate 85b in the form of a fixed object Ga. The fixed object Ga obstructs the falling of other objects of crushing and hence lowers the crushing capacity.
In the meantime, a tooth plate structure which is designed to break an object by bending is known. For example, Japanese Patent Laid-Open (KOKAI) No. 60-147252 (Date of public disclosure: Aug. 3, 1985; Applicant: Kawasaki Jukogyo K.K.) proposes a tooth plate structure which is designed to cut blast furnace slag by bending. However, this tooth plate structure is adapted for breaking by bending only and is not very effective in crushing.